Manganese oxide ceramics and methods for their preparation



United States Patent 3,157,523 MANGANESE 0m CERAMICS AND METHGDS FOR THEE PREPARATIUN Gerhard Bayer, Ohere Hmden, Hinteregg, Zurich, Switzerland, assignor to Givens-Illinois Glass Company, a corporation of Ohio No Drawing. Filed Silly 3, 1961, Se No. 121,344 4 Claims. (Cl. 10565) This invention relates to sintered manganese oxide (Mn O )ceramics and to methods for their preparation. In another aspect, the invention relates to a method for controlling the change of dimensions and porosity in the preparation of Mn O -alumina ceramics. In another aspect of the invention, it relates to a method of making a porous Mn O -alumina ceramic by sintering while obtaining substantially no shrinkage or a slight expansion during the sintering process. In another specific aspect, the invention relates to porous sintered Mn O -a1u1nina ceramics containing 7-20 weight percent alumina.

Pure Mn O ceramics when made by compacting powdered Mn O and sintering undergoes great shrinkage and forms a substantially nonporous body. This shrinkage is a disadvantage in attempting to form ceramic shapes of Mn O of a final desired configuration from the compacted unsintered powders.

It is therefore one object of the invention to provide a method for controlling the shrinkage of Mn O ceramics during sintering. Another object is to provide new Mn o -alumina ceramics. A further object is to provide a method to control the porosity of Mn o -alumina sintered ceramics. Another object is to provide porous Mn O -alumina ceramics and a method for making the same.

Other objects, as well as aspects and advantages, of the invention will become apparent from a study of the specification.

The new ceramics of the invention are prepared by intimately admixing 99 to 80 parts by weight of M11 0 and 1 to 20 parts by weight of A1 0 compacting the admixture and thereafter heat sintering the compacted mixture in an oxidizing (free oxygen-containing) atmosphere. The starting manganese compound need not necessarily be Mn O but can also be a manganese compound which is convertible in situ to Mn O under the conditions of sintering. Temperatures employed in the sintering step are from 1200 to about 1500 C.

Thus, instead of Mn O one can start with MnO, Mn O or MnO since M11304 is the only stable manganese oxide at temperatures above 900 C. in an oxidizing atmosphere, and it does not reoxidize to Mn O or MnO upon cooling down to room temperature. As another example MnCO can be the starting material, since it is decomposed and converted to Mn O under the above sintering conditions. Similarly, decomposable salts such as MnSO can be employed. However, it is usually preferred to use either Mn O or one of the other solid manganese oxides as the starting material in the compacting step.

In the following examples M11 0 and A1 0 of particle size below 60 microns were employed as the starting materials. The Mn O was prepared by heating MnCO at 1000" C. The ceramics were prepared by intimately admixing the powders inthe desired percentages and compacting the mixture at a pressure of 500 kg./cm. followed by s ntering in an air atmosphere for hours at 1380 C., then cooling to room temperature.

Example I The ceramic of this example was a sintered mixture of one weight percent alumina and 99 weight percent Mn O.-,.

The ceramic piece had a linear shrinkage of 16.5% on 1 3,157,523 Patented Nov. 17, 1964 sintering, and was substantially nonporous. A similarly compacted and sintered ceramic of pure Mn O had a shrinkage of 21.5% and was substantially nonporous.

Example 11 Another ceramic was prepared as in Example I but using 5 weight percent alumina and 95 weight percent Mn O The linear shrinkage was 15.5 weight percent and the sintered ceramic was substantially nonporous.

Example III The ceramic of this example was prepared as in Example I except that 10 Wight percent of alumina and 90 weight percent Mn O were used. The resulting ceramic did not shrink during sintering but exhibited a linear expansion of 2.5%. It was also highly porous. This porosity was indicated by the following test. A drop of distilled water (0.03 cc.) was placed from a height of 10 mm. on the surface of a 20 mm. diameter disc of the ceramic. In one second the drop was absorbed completely.

Example IV Example III was repeated except that 20 Weight percent alumina and weight percent Mn O were employed. This ceramic exhibited a linear expansion of 5.5 weight percent during formation. It was also highly porous.

From the foregoing, it will be appreciated that there is provided a method for controlling the change of dimensions and porosity of M11 O -alumina sintered ceramics, which method comprises sintering a compacted powdered intimate admixture of M11 0 and A1 0 at a temperature in the range from 1200 to about 1500 C. in an oxidizing atmosphere and varying the amount of A1 0 within the range from 1 to 20 weight percent in accordance with the shrinkage or expansion desired, the shrinkage decreasing with increasing amounts of A1 0 The exact shrinkage obtained according to the inven-' tion is also dependent in part on a number of factors, including time and temperature of sintering and the particle size of the Mn O and A1 0 However, every other condition being held the same, the effect of alumina content is a very large factor in determining the linear shrinkage.

In the process of the invention the powdered raw materials desirably are below 200 microns particle size, preferably below 80 microns.

In making the porous ceramics of the invention from about 7 to 20 parts by weight percent of alumina are used to about 80 to 93 parts by weight percent of Mn O as the starting material.

In one aspect of the invention a method is provided for producing, by sintering, a porous Mn O A1 O ceramic whereby substantially no expansion or shrinkage is obtained as a result of said sintering step. This method comprises heating A1 0 and Mn O powders in compacted intimate admixture at a sintering temperature in the range from 1200 C. to about 1500 C. in the oxidizing atmosphere and using a ratio of A1 0 to M11 0 within the range from about 7/93 to about 10/90. It will be understood that the exact percentage of alumina employed to obtain substantially zero dimensional change depends on the other factors mentioned, i.e., state of subdivision and the particular time and temperature of sintering. However, the exact percentage can be determined from a series or" routine tests, as will be readily understood.

Although the exact constitution of the present ceramics in their heat reacted form is not known, it is probable that at least some compound is formed between the starting materials. This could account for the unusual change of shrinkage with increasing percentages of alumina.

without departing from the spirit and scope of closure or from the scope of the claims.

7 a; Times of sintering at the temperatures. in the range from 1200 C. to about 1500 C. range usually from r p 1300" 0101450 c.

The present ceramics are generally useful where high temperature resistant ceramics and refractories are conventionally employed. However, the porous ceramics of the invention are especially useful as filters and'diaphragms for alkaline solutions, having superior chemical resistance to such materials. porous ceramics with little or no dimensional change is useful in obtaining articles of very accurate dimensions without need for subsequent machining. The dense or substantially nonporous ceramic products are useful refractories for steam regenerators for recovering heat from high temperature process gases. In combination with the porous ceramics of the invention excellent filters can be constructed with resistance to alkaline solution.

As will be evident to those skilled in the art, various modifications of this invention can be made or'follo'wed The process for obtaining 7 in thelight of the foregoing disclosure and discussion 7 the disb i phere, said manganese compound being selected from the group consisting of M11 0 and a compound convertible to Mn O under the conditions of sintering, the ratio of A1 0 to manganese compound being such that the ratio of A1 0 to Mn O equivalent of said manganese compound is from 1/99 to 1/4.

2. A porous ceramic product according to claim 1 V wherein said ratio is from 7/93 to 1/4;

3. A method of making, by sintering, a porous M11 0 oxidizing atmosphere, the ratio of A1 0 toMn O being in the range from about 7/93 to about 10/90.

4-. A method of making Mn O -alumina sintered ceramics so as to control the change of dimensions and porosity thereof which comprises sintering a compacted powdered intimate admixture consisting essentially of Mn 0 and A1 0 at a temperature in the range from 1200 to about 1500" 'C. ina free oxygen-containing oxidizing atmosphere with a ratio of alumina to M11 0 being in the range from 1/99 to 1/4 in accordance with the type and degree of dimensionalchange desired.

References Cited in the file of this patent UNITED STATES PATENTS 2,152,656 McDougal et al Apr. 4, 1939 

1. A CERAMIC PRODUCT MADE BY SINTERING A COMPACTED INTIAMTE ADMIXTURE CONSISTING ESSENTALLY OF PARTICULATE ALUMINA AND A PARTICULATE MANGANESE COMPOUND AT A SINTERING TEMPERATURE IN THE RANGE FROM 1200 TO ABOUT 1500*C., IN A FREE OXYGEN-CONTAINING OXIDIZING ATMOSPHERE, SAID MAGANESE COMPOUND BEING SELECTED FROM THE GROUP CONSISTING OF MN3O4 AND A COMPOUND CONVERTIVLE TO MN3O4 UNDER THE CONDITIONS OF SINTERING, THE RATIO OF AL2O3 TO MANGANESE COMPOUND BEING SUCH THAT THE RATIO OF AL2O3 TO MN3O4 EQUIVALENT OF SAID MAGANESE COMPOUND IS FROM 1/99 TO 1/4. 